FAP-α is an effective tool to evaluate stroma invasion of lung adenocarcinoma.

The main difficulty in the diagnosis of atypical in situ adenocarcinoma lies in the distinction between true and false stromal invasion. Moreover, how to identify local alveolar wall collapse in situ lung adenocarcinoma and how to identify whether the trapped adenoid structure around scar is an invasion component have become the key points for accurate diagnosis of lung adenocarcinoma. In the present study, we detected 40 cases of lung adenocarcinoma in situ and 40 cases of invasive adenocarcinoma by using immunohistochemical techniques. We found FAP-α had not immunreactivity in the stroma of adenocarcinoma in situ. However, it stained in the stroma of invasive areas in lung adenocarcinoma. FAP-α staining pattern could represent hyperplastic myofibroblast and demonstrated the true invasion of stroma. This study provides strong evidence that FAP-α is an effective tool to evaluate the presence or absence of stroma invasion of lung adenocarcinoma. Our findings will contribute to the accurate diagnosis of lung invasive adenocarcinoma.